cmd: make sure there are no crashes in no api data is returned

Make sure that snap refresh/install does not crash if a change has no
api data. This is not happening in usual interactions with the store,
but it does in some cases when we use the fakestore, which is breaking
some integration tests.

cmd/snap/cmd_snap_op.go

@@ -727,7 +727,8 @@ func (x *cmdInstall) installMany(names []string, opts *client.SnapOptions) error
 		return err
 	}
 
-	if changedSnaps.hasChanges() {
+	// changedSnaps might be nil in some operations with the fakestore
+	if changedSnaps != nil && changedSnaps.hasChanges() {
 		if err := showDone(x.client, chg, changedSnaps, "install", opts, x.getEscapes()); err != nil {
 			return err
 		}
@@ -740,8 +741,10 @@ func (x *cmdInstall) installMany(names []string, opts *client.SnapOptions) error
 
 	// show skipped
 	seen := make(map[string]bool)
-	for _, name := range changedSnaps.names {
-		seen[name] = true
+	if changedSnaps != nil {
+		for _, name := range changedSnaps.names {
+			seen[name] = true
+		}
 	}
 	for _, name := range names {
 		if !seen[name] {
@@ -846,7 +849,8 @@ func (x *cmdRefresh) refreshMany(snaps []string, opts *client.SnapOptions) error
 		return err
 	}
 
-	if changedSnaps.hasChanges() {
+	// changedSnaps might be nil in some operations with the fakestore
+	if changedSnaps != nil && changedSnaps.hasChanges() {
 		return showDone(x.client, chg, changedSnaps, "refresh", opts, x.getEscapes())
 	}
 

cmd/snap/cmd_snap_op_test.go

@@ -2837,6 +2837,89 @@ func (s *SnapOpSuite) TestInstallMany(c *check.C) {
 	c.Check(n, check.Equals, total)
 }
 
+func (s *SnapOpSuite) TestInstallManyNoChanges(c *check.C) {
+	total := 3
+	n := 0
+	s.RedirectClientToTestServer(func(w http.ResponseWriter, r *http.Request) {
+		switch n {
+		case 0:
+			c.Check(r.URL.Path, check.Equals, "/v2/snaps")
+			c.Check(DecodedRequestBody(c, r), check.DeepEquals, map[string]interface{}{
+				"action":      "install",
+				"snaps":       []interface{}{"one", "two"},
+				"transaction": string(client.TransactionPerSnap),
+			})
+
+			c.Check(r.Method, check.Equals, "POST")
+			w.WriteHeader(202)
+			fmt.Fprintln(w, `{"type":"async", "change": "42", "status-code": 202}`)
+		case 1:
+			c.Check(r.Method, check.Equals, "GET")
+			c.Check(r.URL.Path, check.Equals, "/v2/changes/42")
+			fmt.Fprintln(w, `{"type": "sync", "result": {"status": "Doing"}}`)
+		case 2:
+			c.Check(r.Method, check.Equals, "GET")
+			c.Check(r.URL.Path, check.Equals, "/v2/changes/42")
+			fmt.Fprintln(w, `{"type": "sync", "result": {"ready": true, "status": "Done", "data": {}}}`)
+		default:
+			c.Fatalf("expected to get %d requests, now on %d", total, n+1)
+		}
+
+		n++
+	})
+
+	rest, err := snap.Parser(snap.Client()).ParseArgs([]string{"install", "one", "two"})
+	c.Assert(err, check.IsNil)
+	c.Assert(rest, check.DeepEquals, []string{})
+	// note that (stable) is omitted
+	c.Check(s.Stdout(), check.Matches, `(?sm).*one already installed`)
+	c.Check(s.Stdout(), check.Matches, `(?sm).*two already installed`)
+	c.Check(s.Stderr(), check.Equals, "")
+	// ensure that the fake server api was actually hit
+	c.Check(n, check.Equals, total)
+}
+
+func (s *SnapOpSuite) TestRefreshManyNoChanges(c *check.C) {
+	total := 3
+	n := 0
+	s.RedirectClientToTestServer(func(w http.ResponseWriter, r *http.Request) {
+		switch n {
+		case 0:
+			c.Check(r.URL.Path, check.Equals, "/v2/snaps")
+			c.Check(DecodedRequestBody(c, r), check.DeepEquals, map[string]interface{}{
+				"action":      "refresh",
+				"snaps":       []interface{}{"one", "two"},
+				"transaction": string(client.TransactionPerSnap),
+			})
+
+			c.Check(r.Method, check.Equals, "POST")
+			w.WriteHeader(202)
+			fmt.Fprintln(w, `{"type":"async", "change": "42", "status-code": 202}`)
+		case 1:
+			c.Check(r.Method, check.Equals, "GET")
+			c.Check(r.URL.Path, check.Equals, "/v2/changes/42")
+			fmt.Fprintln(w, `{"type": "sync", "result": {"status": "Doing"}}`)
+		case 2:
+			c.Check(r.Method, check.Equals, "GET")
+			c.Check(r.URL.Path, check.Equals, "/v2/changes/42")
+			fmt.Fprintln(w, `{"type": "sync", "result": {"ready": true, "status": "Done", "data": {}}}`)
+		default:
+			c.Fatalf("expected to get %d requests, now on %d", total, n+1)
+		}
+
+		n++
+	})
+
+	rest, err := snap.Parser(snap.Client()).ParseArgs([]string{"refresh", "one", "two"})
+	c.Assert(err, check.IsNil)
+	c.Assert(rest, check.DeepEquals, []string{})
+	// note that (stable) is omitted
+	c.Check(s.Stdout(), check.Equals, "")
+	c.Check(s.Stderr(), check.Equals, "All snaps up to date.\n")
+	// ensure that the fake server api was actually hit
+	c.Check(n, check.Equals, total)
+}
+
 func (s *SnapOpSuite) TestInstallZeroEmpty(c *check.C) {
 	_, err := snap.Parser(snap.Client()).ParseArgs([]string{"install"})
 	c.Assert(err, check.Not(check.IsNil))